Role of visual information and learning in habitat selection by a generalist parasitoid foraging for concealed hosts

Abstract

Generalist species usually have to deal with a larger variety of cues during habitat selection than do specialists, and thus, learning has been proposed as a highly profitable strategy to find the most suitable habitat. We analysed the effect of previous experience on the use of visual information by the wasp Diachasmimorpha longicaudata, a generalist fruit fly larval parasitoid, in the context of host habitat selection. These parasitoids search for hosts concealed in plant structures, so visual cues from the hosts' environment could play a key role in host finding. We also studied how different visual cues used by this species interact and affect the habitat choices of female wasps. We studied three forms of visual cues: colour, shape and size. All experiments were conducted under controlled laboratory conditions, using artificial models mimicking fruit. Naïve females showed no preference pattern for colour or shape, but they showed a clear preference for larger models. These results were unaffected when females were previously exposed to host larvae (no sensitization effect). Associative learning was found for colour: tested females developed a clear pattern of preferences after they were exposed to larvae associated with a particular colour. We found that colour and size have a similar effect on the female's choice, and that this effect is neither additive nor multiplicative. Our findings emphasize the importance of both visual cues during host habitat searching by D. longicaudata and the influence of learning on the preference patterns of a generalist parasitoid.